Anti-skid control system for an automotive vehicle

Abstract

The invention is directed to an anti-skid control system for controlling a braking force applied to each of the road wheels with a hydraulic braking pressure supplied to a wheel brake cylinder through pressure control means. A wheel speed of each of the road wheels is detected. Then, an estimated vehicle speed for each of the road wheels is calculated on the basis of the wheel speed and a decreasing rate of estimated vehicle speed for at least one of the road wheels other than the road wheel for which the estimated vehicle speed is being calculated. The estimated vehicle speed is, therefore, prevented from being set largely below the actual speed of the vehicle. The pressure control means is provided for increasing, holding or decreasing the hydraulic braking pressure in response to a result of comparison between the estimated vehicle speed and the wheel speed for each of the road wheels.

What is claimed is: 
     
       1. An anti-skid control system for an automotive vehicle having a wheel brake cylinder mounted on each of a plurality of road wheels for applying a braking force thereto and a master cylinder for supplying a hydraulic braking pressure to said wheel brake cylinder, comprising: means for detecting wheel speed of each of said road wheels and providing an output signal corresponding to said wheel speed;   means for calculating an estimated vehicle speed for each of said plurality of road wheels on the basis of said wheel speed of each of said plurality of road wheels;   means for calculating a decreasing rate of said estimated vehicle speed of each of said plurality of road wheels;   means for modifying said estimated vehicle speed to provide a standard estimated vehicle speed for each of said plurality of road wheels in response to the decreasing rate of said estimated vehicle speed of at least one of said plurality of road wheels other than said estimated vehicle speed to be modified;   means for comparing said standard estimated vehicle speed and said wheel speed for each of said plurality of road wheels; and   pressure control means for increasing, holding or decreasing said hydraulic braking pressure in response to a comparison between said standard estimated vehicle speed and said wheel speed for each of said plurality of road wheels.   
     
     
       2. An anti-skid control system for an automotive vehicle as set forth in claim 1, wherein said means for modifying said estimated vehicle speed modifies said estimated vehicle speed to provide said standard estimated vehicle speed for each of said plurality of road wheels on the basis of a minimum decreasing rate of the decreasing rates of said estimated vehicle speeds of said plurality of road wheels other than said estimated vehicle speed to be modified. 
     
     
       3. An anti-skid control system for an automotive vehicle as set forth in claim 1, wherein said means for modifying said estimated vehicle speed limits the decreasing rate of said estimated vehicle speed to provide said standard estimated vehicle speed for each of said plurality of road wheels in response to the decreasing rate of said estimated vehicle speed of at least one of said plurality of road wheels other than said estimated vehicle speed to be modified. 
     
     
       4. An anti-skid control system for an automotive vehicle having a wheel brake cylinder mounted on each of road wheels for applying a braking force thereto and a master cylinder for supplying a hydraulic braking pressure to said wheel brake cylinder, comprising: means for detecting a wheel speed of each of said road wheels and providing an output signal corresponding to said wheel speed;   means for calculating wheel acceleration of each of said road wheels from said wheel speed;   means for calculating an estimated vehicle speed for each of said road wheels on the basis of said wheel speed of each of said road wheels;   means for calculating a decreasing rate of said estimated vehicle speed of each of said road wheels;   means for modifying said estimated vehicle speed to provide a standard estimated vehicle speed for each of said road wheels in response to the decreasing rate of said estimated vehicle speed of at least one of said road wheels other than said estimated vehicle speed to be modified;   means for calculating a difference between said wheel speed and said standard estimated vehicle speed;   means for setting a wheel lock rate indicative of a locking condition of each of said road wheels on the basis of at least said difference between said wheel speed and said standard estimated vehicle speed;   means for setting an increasing time for increasing said hydraulic braking pressure supplied to said wheel brake cylinder and a holding time for holding said hydraulic braking pressure with a proportion between said increasing time and said holding time determined in response to a relationship between said wheel acceleration and said wheel lock rate, and setting a decreasing time for decreasing said hydraulic braking pressure and said holding time with a proportion between said decreasing time and said holding time determined in response to a relationship between said wheel acceleration and said wheel lock rate; and   pressure control means for alternately increasing and holding said hydraulic braking pressure supplied to said wheel brake cylinder in response to said increasing time and said holding time, or alternately decreasing and holding said hydraulic braking pressure in response to said decreasing time and said holding time.   
     
     
       5. An anti-skid control system for an automotive vehicle as set forth in claim 4, wherein said means for modifying said estimated vehicle speed modifies said estimated vehicle speed to provide said standard estimated vehicle speed for each of said road wheels on the basis of a minimum decreasing rate of the decreasing rates of said estimated vehicle speeds of said road wheels other than said estimated vehicle speed to be modified. 
     
     
       6. An anti-skid control system for an automotive vehicle as set forth in claim 4, wherein said means for modifying said estimated vehicle speed limits the decreasing rate of said estimated vehicle speed to provide said standard estimated vehicle speed for each of said road wheels in response to the decreasing rate of said estimated vehicle speed of at least one of said road wheels other than said estimated vehicle speed to be modified.